If confirmed, the claims could cast a pall over the National Front congress next weekend aimed at recasting the party's image after a series of setbacks since Le Pen lost to Emmanuel Macron in last year's presidential race.
The party is suspected of using money from Brussels earmarked for parliamentary assistants to pay staff for party work in France.
The Journal du Dimanche newspaper said the two French judges looking into the suspected EU funding scandal now think it may have been carried out from July 2009 into 2012.
That would mean nearly seven million euros ($8.6 million) was potentially misused, up from a previous estimate of some five million euros.
Le Pen was charged last June with breach of trust over the salaries paid to her chief of staff Catherine Griset and her bodyguard Thierry Legier, and for complicity in breach of trust as FN leader.
She is one of 17 National Front lawmakers -- along with her estranged father Jean-Marie Le Pen -- being investigated over salaries paid to around 40 parliamentary assistants.
If tried and convicted, she faces up to three years imprisonment and a fine of up to 375,000 euros, though it is unlikely she would receive a custodial sentence.
Le Pen is running unopposed for a third term as the National Front leader at a congress in Lille, northern France, on March 10 and 11. She will propose changing the party's name in a bid to break with its past association with overt racism and anti-Semitism.
Last week she was charged over posting on Twitter gruesome images of purported atrocities by Islamic State jihadists just a few weeks after the Paris terror attacks in November 2015.
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